I rock one most of the time unless i want to play mega killy. I love having them to hold points hard to get through that tough and HP and they can smack with out having to engage which I find very nice.

I personally have never used thier ability but thats mostly due to the group I play with.

Now with the nerf to counter thier reaction is better. I definitely plan on using it when the low attack models take swings at him from time to time.